The daily transport of human plasma apoA-I and apoA-II, triglyceride and total cholesterol from the thoracic duct lymph into plasma was measured in two subjects prior to and three subjects subsequent to renal transplantation. Lymph triglyceride transport was approximately 83% of the daily ingested fat loads while lymph cholesterol transport was consistently greater than the amount of daily ingested cholesterol. Lymph apolipoprotein transport exceeded the predicted apolipoprotein synthesis rate by an average of 659 plus or minus 578 mgs/day for apoA-I and 109 plus or minus 59 mg/day for apoA-II among the five subjects. Lymph HDL particules are mostly HDL2b and HDL2a and have a greater triglyceride and smaller cholesterol ester content when compared to homologous plasma HDL. The major quantity of both lymph apoA-I (81 plus or minus 8%) and apoA-II (90 plus 11%) was found within HDL with almost all of the remainder found in chylomicrons and VLDL. The combined results are consistent with a major contribution of the intestine to total body synthesis of apoA-I and apoA-II. An important role of lymph in returning filtered apolipoprotein to plasma in association with HDL is proposed.